At present, light-polarizing films are produced by adsorbing iodine or one or more dichroic dyes as polarizing matters on a film of polyvinyl alcohol (hereinafter referred to as "PVA") or a derivative thereof oriented by stretching or a polyenic film obtained by orienting a polyene formed by dehydrochlorination of a polyvinyl chloride (hereinafter referred to as "PVC") film or dehydration of a PVA based film.
Light-polarizing films using iodine as a polarizing matter are excellent in initial polarization quality but weak to water and heat and, hence, involve a problem in durability in the case of using the film under high-temperature and high humidity conditions for a long period of time. When PVA is used for the light-polarizing film, for improving the durability, there may be considered a method of fast treatment with an aqueous solution containing formalin or boric acid or a method of using a polymer film having a low water vapor transmission as a protective film, but the light-polarizing films by such an improvement are yet insufficient in durability under high-temperature and high-humidity conditions.
Also, light polarizing films using dichroic dyes as polarizing matters are improved in durability under high temperature and high-humidity conditions as compared with light polarizing films using iodine as a polarizing matter, but the improvements are not still satisfactory in the case of using PVA as a base film thereof.